This invention relates to the preparation and structure of filters for removing particulates from fluids, and, more particularly, to a cylindrical filter made from a ceramic having carefully sized open-celled porosity
A filter is a device that removes solid matter from a fluid stream, either a gas or a liquid. Filters are primarily of two types. A screen-type filter creates an obstacle to passage for solid matter larger than the mesh size of a screen. A depth- or media-type filter presents a tortuous path through which the fluid and the entrained solid matter must pass. Solid matter is removed by adherence to the interior walls of the passageway. The media filter is able to remove solid matter smaller than the passageway size. The present invention deals with a filter that removes particulate from a fluid stream by both mechanisms.
The media filter must be constructed of a material that withstands the environmental conditions presented by the fluid stream, such as high temperatures, erosion, and corrosion. It must also have a reliably defined internal passageway structure through which the fluid passes. If the passageways have too large a size or provide too direct a path through the filter body, particles will pass through the filter. If the passageways have too small a size or too indirect a path, the filter presents too great a flow resistance to the fluid and becomes unacceptable as an element in a flow stream. The filter must be fabricated at an acceptably low cost for the particular application.
In some applications, the media filter must be able to withstand high fluid temperatures. The filter element must therefore be made of a ceramic material with a pattern of filtering passageways through the filtration membrane. Ceramic filter membranes can be prepared by loosely packing ceramic powders or using the right combination of sintering modifiers mixed with the ceramic powders. When such a mass is sintered (fired), porosity intentionally remains within the structure and provides the path through which the fluid flows. With this approach it is difficult to attain exactly the desired type of internal path. Even where the desired passageway structure is attained, assembling the filter elements with their supports, end plates, etc. into a filter structure may be difficult due to the difficulties in attaining reliable ceramic-to-metal or ceramic-to-ceramic seals.
There remains a need for a reliable, economically fabricated media filter utilizing ceramic filter elements. Such a filter must have a reliably fashioned internal passageway structure that is reproducible in the sense that each filter will achieve substantially the same filtering action and present the same flow resistance to fluids passing through the filter. The present invention fulfills this need, and further provides related advantages.